FR2698503A1 - Digital circuit for extracting phase and envelope signals from a single sideband signal. - Google Patents

Abstract

The circuit includes first means (1, 2, 3, 4, 5) for transforming the low frequency signal into a sampled single sideband signal coupled to second means (6, 7, 8) for separating the sampled SSB signal into its two phase and envelope components. Application: SSB transmitter.

Description

Digital circuit for extracting phase and envelope signals

  a single sideband signal

  The present invention relates to a digital circuit for the extrac-

  phase and envelope signals of a single sideband signal.

  It is known to obtain a modulated signal according to the principle of

  single-sideband modulation, hereinafter referred to as SSB, to separate the SSB signal into its two phase and envelope components in order to apply them using two distinct paths on a first and a second input of the modulation stage of a power stage of a transmitter. Such devices are for example described in US Patent 2,666,133 filed in the name of Mr. KHAN or in the

  European patent application O 202 985 filed in the name of the

  Other devices operating on this same principle are also known from the publication of M. Leonard KHAN in the journals Processing of the Vol.

  "Single sideband transmission by enclosure elimination and

  "or" by the same author entitled "Compatible

  single side band "also published in the journal l R E in July 1961.

  The main disadvantage of these devices is that they require in particular short-wave broadcasting applications

  very stable quartz and therefore very expensive to make the fil-

  one of the two sidebands that are only 300 Hz away from each other around a carrier frequency around a few M Hz. Although fully digital bandpass filters have been they are inapplicable because they are very difficult to achieve Recursive filters see indeed their performance limited by the poles of their transfer function having a module very close to the unit circle which lead to instabilities By cons use non-recursive filters, which is in essence a guarantee of stability, requires computation times that are all the more important since their

  number of calculation points is higher. For example, for

  to kill an attenuation of 40 d B of the lower lateral band it is necessary with this solution to use a finite impulse response filter determined by 4000 points, which is unfortunately incompatible with the transmission times of the receivers Hilbert filter solutions are not can not be considered because it is very difficult to obtain a

  gain of 1 with a phase shift of 900 more to obtain attenua-

  lateral band below 40 d B with variations in

  around 900 not exceeding 1.14, these relations require theo-

  only a few megahertz sampling frequencies

  which can not be realized in practice.

  The object of the invention is to overcome the aforementioned drawbacks.

  For this purpose, the subject of the invention is a digital circuit for the ex-

  pulling phase and envelope signals from a sideband signal

  unique, obtained from a low frequency signal sampled

  characterized in that it comprises first means for transforming the low frequency signal into a sampled single sideband signal

  coupled with second means for separating the sample SSB signal.

  lonned in its two components of phase and envelope.

  Other features and advantages of the invention will appear in

  with the following description made with reference to the accompanying drawings which

represent:

  FIG. 1 is a block diagram of a device according to the invention.

  tion; FIG. 2 is a filter template implemented by the invention; FIG. 3 is an example of a sinusoidal signal modulated in phase with the device according to the invention; FIG. 4 an embodiment of a device according to the invention

  using four signal processors.

  The device according to the invention which is represented in a functional form in FIG. 1 comprises a first 1 and a second 2 filtering network fed both by a sequence Sn of digital samples of a frequency BF signal Fel. organization networks 1 and 2 transform the sequence Sn of samples into a complex sequence of samples SA (n) such that S An) = SR (n) + JSI (n) The samples SR (n) of the real part of the following are obtained at the output of the network 1 and the samples Sl (n) of the imaginary part are obtained at the output of the network 2 The networks 1 and 2 are respectively coupled to a first input denoted "+" and a second input denoted "- of an adder circuit 3 by means of two multiplier circuits 4 and 5 to multiply the complex sequence SA (n) by a sequence of complex numbers defined by the relation cos (2 rn F 0) + j sir (2 rn Fo) (1) keeping only the real part Sm (n) of the result obtained This calculation is performed by the multiplier circuit 4 which produces the product SR (n) cos (2 rn Fo) and by the multiplier circuit 5 which produces the product

  Sl (n) sin (27 n Fo) The sequence Sm (n) which is thus obtained at the exit of the cir-

  adder cook 3 is a sampled modulated SSB signal of the form S n (rn = SR (n) cos (2c Fo) S, (r si (2 icn F 0) (2) The signal Sm (n) is applied to the input of a summing circuit 6 which carries out the vector sum in the Fresnel plane of the samples Sm (n) with the frequency signal Fo This signal is applied on the one hand to the input of a clipper 7 which supplies the phase component and secondly, at the input of a filter 8 via a multiplier circuit 9

  to extract the envelope signal.

  Networks 1 and 2 each have a set of 3 expansions

  first order 101 and 102 whose pole modulus is deter-

  in accordance with the sampling frequency Fel of the low frequency signal and an interpolation circuit 111 and 112 of the signal obtained at the output of the phase-shifter operating at the sampling frequency Fe 2 of

  the RF high frequency carrier of the BF signal To obtain an attenuation

  40 d B between the two sidebands the constant specific to each phase-shifter is determined so that the phase difference

  p 1- <P 2 existing at the output of each of the phase-shifters 101 and 102 is either

  written inside a filter jig having between two minimum and maximum cut-off frequencies, for example 150 Hz to 4.5 K Hz with a phase shift of 90 not exceeding a phase variation of 1, 14 as is represented in FIG. 2 The clipper 7 is in turn determined to provide a sinusoidal signal modulated in phase following a

  similar in shape to that shown in Figure 3.

  Naturally, the embodiment of the device according to the invention

  described above is not unique, it goes without saying that the functionalities

  of this device can be achieved quite otherwise

  using, as shown in Figure 4, a set of process

  signal strengths respectively 13, 14, 15 and 16 coupled by

  data and address entries to a RAM 17 A converts

  analog-to-digital converter 18 converts the BF signal into

  These digital signals are applied to the inputs of the

  13 and 14 These respectively calculate the

  real signals SR (n) and imaginary JSI (n) of the preceding relation (2).

  These samples obtained are stored in the RAM 17 and their amplitude is then smoothed by the signal processor 15 to calculate

  the signal signal of the SSB signal.

  corresponding loppe are applied to a digital-analog converter

  18 to form the signal signal of the SSB signal.

  The phase dule is calculated by the signal processor 16 from the samples stored in the random access memory 17 which cleaves the samples by detecting the sign of each of them. The sinusoidal signal is reconstructed from the phase-modulated samples.

  provided by the processor 16 by means of a digital-to-digital converter

analog 19.

Claims (4)

  A digital circuit for extracting phase and envelope signals from a single sideband signal obtained from a sampled low frequency signal, characterized in that it comprises first means (1, 2, 3, 4, 5, 13, 14) to transform the signal   low frequency into a single sideband signal sampled   second means (6, 7, 8, 15, 16, 17, 18) to separate the   SSB signal sampled into its two components of phase and enve- Loppe.   Circuit according to Claim 1, characterized in that the first   means include a first (13) and a second (14) process   signal sources to compute from the low-frequency signal sampled   two sets of samples SR (n> and Si (n) respectively real and imaginary.   Circuit arrangement according to Claim 2, characterized in that the second means comprise third storage means (17) for storing each of the two sets of samples SR (n) and S (n) respectively coupled to a third (15) processor. signal for calculating the SSB signal envelope signal and at a fourth (16)   signal processor for calculating the phase modulated signal.   Circuit according to Claim 1, characterized in that the first first means include:   a first (1) and a second (2) filtering network for transmitting   to form the low frequency signal sampled Sn into two   sample plexes with real SR (n) and imaginary Si (n),   an adder circuit (3) coupled respectively by a first   first input noted (+) and a second input noted (-) at the outputs of the first (1) and second (2) networks via two multiplier circuits (4) and 5) to multiply the complex sequence SA (n) formed of the imaginary parts SR (n) and Si (n) by a third sequence of numbers   complexes representing the frequency carrier Fo of the signal BLU and ob-   hold at the output of the adder circuit (3) a sample modulated SSB signal   Sm (n) of the form: S m (n) = SR (n) Cos (27 rn Fo) S 1 (n) sin (2 n Fo) a summing circuit (6) coupled to the output of the adder circuit ( 3) to perform the vector sum in the Fresnel plane of the   samples Sm (n) with the frequency carrier Fo and a skimming circuit   (7) coupled to the output of the summing circuit (6) to provide the phaser of the BLU signal.   Circuit according to Claim 4, characterized in that it comprises a filter circuit (8) coupled to the input and the output of the clipping circuit   (7) via a multiplier circuit (9) to extract the health of BLU signal envelope.